1. Technical Field
This invention relates to cylinder liners for diesel engine applications.
2. Related Art
Historically, heavy duty diesel engines have employed replaceable cylinder liners made of various grades of cast iron. Cast iron is selected for its low production cost and good wear resistance due to the presence of free graphite at the running surface which acts as a lubricant. Increased wear resistance in the cylinder bore can be achieved by hardening the base cast iron alloy to create a martensitic microstructure.
For traditional cast iron liners, it has been demonstrated that under conditions of exhaust gas recirculation, or EGR, in which some of the exhaust gases are recirculated back into the cylinder for further combustion with the fresh fuel mix, the liners have shown accelerated wear in comparison to the same liners operating under non-EGR conditions. One contributing factor is that recirculated diesel exhaust contains abrasive particles and promotes the formation of various corrosive acids within the combustion chamber which are prone to attacking cast iron liners.
In addition to the wear considerations of cast iron liners, the requirement for ever-increasing emissions regulation has the effect of reducing the performance of the engines. This, coupled with the drive to yield ever-increased power from its engines, has caused diesel engine manufactures to increase the displacement of the cylinders in order to compensate for the power loss due to EGR. One solution is to thin the liners to increase the bore size while avoiding having to increase the size of the engine block. However, there is a limit as to how thin a cast iron liner can be made and still function properly. In particular, cast iron liners of thinner wall sections are prone to cavitation and distortion because the cast iron is a relatively porous material with free graphite present at the surface.
It is known to employ steel cylinder liners, but these are not know to be suitable designed for use in a heavy-duty wet linered diesel engine applications, where the temperatures are high and the peak cylinder pressures can reach 220 bar or more. These prior steel liners are known to be either of the dry liner variety (i.e., no water cooling) or of the air-cooled variety for aircraft usage.